Surveillance systems or other monitoring systems allow to identify people and objects in a surveyed or monitored area. In some situations, it may be desirable to send a message, for example an SMS, to the mobile device of an observed person who is walking around in the area. Such a situation may occur when a person left behind a personal object or when people should be warned about a dangerous situation in the direction they are heading to, e.g. a sudden manifestation or hooliganism. It may also be desirable to send a message to a communication device installed in a car or any other vehicle, for example to the on-board computer of a car equipped with cellular functionality. The problem in these situations is to retrieve the identification of the communication device such as for example the phone number or email address.
Several solutions exist for identifying and sending messages to mobile and communication devices in such situations. A first solution proposed in US20030013466A1 is by using cell broadcasts, designed for simultaneous delivery of a message to multiple users in a specified area. In other words, an operator can send a text message to all users within reach of a particular cell tower and thus a particular area. A disadvantage however is that there are no means to distinguish between people or objects, for example, based on their moving trajectories. A further disadvantage is that the broadcast perimeter and, hence, the accuracy of addressing specific persons largely depends on the number and range of available radio beacons covering an area.
Another solution uses public cameras in combination with face recognition algorithms to identify persons. The system then looks up a mobile phone number associated with a person in a database and sends a text message to the targeted person or persons. A disadvantage of this solution is that the personal details like the phone number, photo and name of the persons have to be known to the monitoring or surveying system, compromising the privacy of the persons. A further disadvantage of this solution is that it is only applicable for persons and objects that can be identified through a camera, e.g. requiring that the face of a person or the license plate of a car is clearly visible in camera feeds which is not always the case.